The present disclosure is related to air filtering systems for intake air for low temperature catalytic processes, such as a fuel cell. In particular, the disclosure is directed to a filter assembly that removes particulate and chemical contaminants from the intake air, and that also provides sound attenuation.
Practical and efficient generation of electrical energy has been sought since the discovery of electricity. Hydroelectric, fossil fuel and nuclear generation plants and batteries have long been used to supply our electrical power needs. Power generation by use of fuel cells is a relatively recent development that is rapidly gaining acceptance for both commercial and residential applications. As compared with conventional fossil fuel burning powered sources, they are relatively clean and efficient. Fuel cells are electrochemical devices that efficiently convert a fuel""s chemical energy directly to electrical energy. They chemically combine a fuel and oxidant without burning, thereby eliminating many inefficiencies and most pollution of traditional combustion power systems.
A fuel cell operates in principle much like a battery. However, unlike a battery, a fuel cell does not run down or require recharging. It will continue to produce energy in the form of electricity and heat as long as fuel is supplied to it. In general, a fuel cell consists of two electrodes (an anode and a cathode) sandwiched around an electrolyte. Hydrogen and oxygen are passed over the anode and cathode electrodes respectively in a manner that generates a voltage between the electrodes, creating electricity and heat, and producing water as the primary by-product.
The hydrogen fuel is supplied to the anode of the fuel cell. Some consume hydrogen directly, while others use a fuel reformer to extract the hydrogen from, for example, a hydrocarbon fuel such as natural gas, methanol, ethanol, or gasoline. Oxygen enters the fuel cell at the cathode. The oxygen can be supplied in purified form or can come directly from atmospheric air.
The fuel cell uses a catalyst to cause the hydrogen atom to split into a proton and an electron, each of which takes a different path to the cathode. The protons pass through the electrolyte. The electrons create a useful electric current that can be used as an energy source, before returning to the anode where they are reunited with the hydrogen protons and the oxygen to form water.
Fuel cells are generally characterized by the electrolyte material which is sandwiched between the cathode and anode, and which serves as a bridge for ion exchange. There are five main known types of fuel cells. Alkaline fuel cells (AFCs) contain a liquid alkaline electrolyte and have been used primarily in space mission applications. Proton exchange membrane fuel cells (PEMFCs) contain a solid polymer electrolyte. Their low temperature operation, high power density with the ability to vary their output quickly to meet shifts in power demand make their use ideal for both mobile and stationary applications, such as powering vehicles or buildings. Phosphoric acid fuel cells (PAFCs) utilize a phosphoric acid electrolyte and are currently used for commercial power generation. Molten carbonate fuel cells (MCFCs) contain a carbonate salt electrolyte, which becomes molten at the operating temperature of about 650xc2x0 C. Solid oxide fuel cells (SOFCs) use a ceramic electrolyte material and operate up to about 1000xc2x0 C. Both the MCFCs and the SOFCs can use carbon monoxide as fuel.
Fuel cells have a vast range of potential applications. They can be used to produce electricity for homes, businesses and industries through stationary power plants ranging in size from, for example, 100 watts to several mega watts. Fuel cells produce a direct current (dc) that must be inverted to alternating current for grid-connected applications or for use with most consumer products. However, future fuel cells could be operated in both grid-connected and non-grid-connected modes. For residential applications, smaller fuel cell power plants could be installed for the production of both heat and power. They could also be used to provide power to remote residential entities having no access to primary grid power, potentially eliminating the necessity of grid-connections.
In addition to the larger scale power production applications, fuel cells could replace batteries that power consumer electronic products such as laptop computers, cellular phones and the like and could even be micro-machined to provide power directly to computer chips. Another promising commercial application of fuel cells is their potential to replace the internal combustion engine in vehicle and transportation applications. Their applications are virtually unlimited.
All of the known fuel cell configurations discussed above have a common need for oxygen as an integral ingredient for performing the cell""s chemical process. For most commercial applications it is desirable for such oxygen to be supplied directly from the atmospheric air. However, it is accepted that in today""s world, all atmospheric air has some degree of contaminants present in it. Such contaminants can be relatively large such as loose debris, insects, tree blossoms or the like, or can be in the nature of small particulates suspended in the atmosphere such as dust, tree pollen, smog or smoke particulates. Chemical contaminants are also widely present in atmospheric air, whether as a result of man-made pollution or as those which naturally occur. Typical chemical contaminants might include volatile organic compounds such as aromatic hydrocarbons, methane, butane, propane and other hydrocarbons as well as ammonia, oxides of nitrogen, ozone, smog, oxides of sulfur, carbon monoxide, hydrogen sulfide, etc. Since efficient fuel cell operation depends on a delicately balanced chemical reaction, such contaminants in the air used by the cell can have a significant adverse effect on the cell""s operation and, depending on their nature, can even cause the fuel cell to discontinue operation. It is important therefore, that the fuel cell system include a filtration system that is designed to eliminate harmful contaminants and one that enables the fuel cell to be used in a wide range of use environments. Such contaminants may appear intentionally (such as in military environments or by terrorists) or unintentionally. Solution of the latter requirement becomes particularly acute when the fuel cell is used in a mobile application that subjects the fuel cell to many varied atmospheric conditions.
To obtain the amount of oxygen necessary for the fuel cell to produce the desired energy output, it has been found desirable to pass the oxygen-bearing containing air through air movement equipment such as a compressor or fan located within the air flow stream supplied to the fuel cell. Unfortunately, while the fuel cell chemical reaction is a silent process, typical compressors produce significant undesirable and annoying noise levels. It is desirable, therefore, in a fuel cell system to reduce and to minimize the noise produced by and/or transmitted through the compressor and back into the environment in which the fuel cell system operates. Since reduced fuel cell system size is also typically desirable, it is preferable that the filtration and sound attenuation features of the fuel cell system be physically reduced as small as possible and even preferably be combined within a single element or housing. The present invention addresses the above-identified needs and desires for an efficient and quiet fuel cell system for use in a wide variety of applications.
What is desired, therefore, is a fuel cell that functions within environments having a wide range of contaminants.
The present invention provides a filter assembly for filtering the intake air used in low temperature catalytic reactions, such as fuel cells. The assembly provides particulate filtration and chemical filtration to the incoming air stream to provide a purified oxidant to the cathodic side of a catalytic reactor, such as a fuel cell. The filter assembly captures and retains particulate and chemical contaminants that can harm the catalytic process, the electrolyte, or both. Although the operation of the fuel cell is essentially silent, the assembly also provides sound suppression or attenuation for any equipment, such as a compressor, operatively connected with the fuel cell.
In one particular embodiment, the invention is directed to a system for producing power. The system comprises an air filter assembly that comprises a housing and a filter element in the housing. The housing has an inlet and an outlet, the inlet accepting dirty atmospheric air to the filter assembly, and the outlet providing clean air from the filter assembly. The filter element comprises at least a physical or particulate filter portion constructed and arranged to remove particulate contaminants from the dirty air. The filter element may also include a chemical filter portion constructed and arranged to remove chemical contaminants from the dirty air. The filter assembly also includes a sound suppression or attenuation element, which may also be in the housing. The sound suppression element is configured to provide broadband attenuation of the sound passing through the filter assembly.
The system further comprises a fuel cell having an air intake port. The air filter assembly is constructed and arranged to provide clean air from the outlet of the filter assembly to the intake port of the fuel cell. The filter assembly is particularly designed and configured to remove contaminants that might harm or poison the reactions occurring within the fuel cell.
The system generally also comprises equipment, such as a compressor or a blower, to provide enhanced air flow to the equipment, such as the fuel cell. The filter assembly is also particularly arranged to reduce the level of noise emanating from any such equipment and from the fuel cell system to which such equipment may be connected.
In another particular embodiment of the invention, a filter assembly is provided. The filter assembly has a housing and a filter element in the housing. The housing has an inlet and an outlet, the inlet receiving dirty air into the filter assembly, and the outlet providing clean filtered air from the filter assembly. The filter element has a particulate filter portion constructed and arranged to remove physical or particulate contaminants from the dirty air and may have a chemical filter portion constructed and arranged to remove chemical contaminants from the dirty air. The filter assembly also has a sound suppression element, such as a resonator, sonic choke, full choke, sound adsorbent material, that attenuates or otherwise reduces sound by at least 3 dB at one meter, preferably by at least 6 dB.
Such a filter assembly can be used with any process or system that produces noise or sound and that benefits from cleaner intake gas (such as air). A fuel cell system is one power producing system with which filter assembly of the present invention can be used. Additionally, the filter assembly can be used with other power producing systems, such as diesel or gasoline engines.